As is known in the art, wireless Internet access is different from simply accessing the Internet wirelessly. Mobile wireless users have different needs, motivations and capabilities from typical wireline users. For example, a mobile user is usually in a multi-tasking mode, e.g., accessing the Internet while attending a meeting or shopping in the mall. Typical Internet accesses are bursty in nature (checking stock quotes, weather, or finding a nearby restaurant) and task-oriented. Thus, browser-centric applications and elaborate user interfaces are of limited utility since a mobile user usually carries small devices such as a cell phone or a Personal Digital Assistant (PDA) having relatively small displays. These personalized devices, which are typically identified by a wireless network address such as a cellular phone number, provide mobile users with continuous access to the Internet.
Advances in wireless networking and messaging technologies have given mobile users many choices to access Internet contents and services. Existing devices and protocols include personal digital assistants (PDAs), such as Palm Pilots with Web Clipping, cell phones with wireless application protocol (WAP) or short message service (SMS), e-mail devices, such as Blackberry and AT&T PocketNet, supporting Post Office Protocol 3 (POP3) and/or (Internet Message Access Protocol) IMAP, and America On Line (AOL) Instant Messaging (AIM). In mobile applications, it is often desirable to receive multimedia data on mobile devices.
Multimedia data, for example, uncompressed video typically requires transmission bandwidths of tens of megabits per second, and is thus not suitable for bandwidth-limited environments. Even international standards like ISO JPEG, MPEG1 and MPEG2 are also not well suited to such environments. However, recent compression standards, including ITU H.263, MPEG-4 and the in-progress H.26L are targeted towards “reasonable” quality bit rates as low as about 10 kbps. The standards only specify the structure of the bitstream, while leaving a great deal of flexibility in how an encoder creates a compliant bitstream. To control the bit rate and quality of the multimedia data, the encoder can vary processing of the signal prior to source coding, scale of the quantizer, mode selections and frame rate. The wireless multimedia transcoders (encoder/decoder pairs), for example conventional video transcoders are designed to perform under the following constraints: 1) low spatial resolution, 2) low frame rate and 3) slowly moving and low-detail contents. Some of the system design issues that arise in the wireless environment are data rate minimization, complexity, power consumption and reliability.
Implementation complexity and power consumptions are especially important in the design of portable multimedia terminals. The amount of processing required for decoding, for example video data, is related to the number of frames per second (frame rate) and the total number of pixels in one frame (frame size). Therefore, the frame rate and the frame size need to be adjusted to the processing power of the client device.
Wireless access links suffer from severe transmission conditions, such as narrow bandwidth, higher bit error rates and high latency. One of the wireless environment's distinguishing characteristics is signal fading due to changes in the propagation path as the terminal moves and interference from other terminals in the same cell or from neighboring cells. Reliability is measured by the bit error rate (BER). Typical BERs on mobile wireless channels range from 10−2 to 10−3. Thus achieving acceptable reliability requires powerful error detection and correction techniques which are continuously adapted to the changing transmission conditions. Another problem with wireless links is congestion of the control and request channels when these channels are used simultaneously to deliver the multimedia content.
It would, therefore, be desirable to provide personal multimedia services delivered over a wireless communication channel to a variety of mobile device types while minimizing congestion of the control and request paths. It would further be desirable to provide a mobile service platform and separate multimedia servers having distinct channels for delivering transcoded multimedia data and adapting the delivery of the multimedia data to fluctuations of the wireless communication channel conditions. It would also be desirable to enable a mobile user to control multimedia sources.